This invention relates generally to improved processes for preparing squaraine compositions, and more specifically, the present invention is directed to processes for obtaining squaraine compositions of enhanced photosensitivity by accomplishing the reaction involved in the presence of phenols or phenol squaraines. In one embodiment of the present invention there is provided certain known squaraine compositions of enhanced photosensitivity by the reaction of squaric and an aromatic amine in the presence of a phenol or a phenol squaraine, followed by regenerating the crystallized mixture of squaraines by for example known evaporation techniques. The squaraine compositions resulting from these processes are useful for incorporation into layered photoresponsive imaging devices wherein, for example, the sensitivity thereof can be varied or enhanced. These devices are thus responsive to visible light, and infrared illumination needed for laser printing, wherein gallium arsenide diode lasers are selected. Specific photoresponsive device envisioned can, for example, contain situated between a photogenerating layer and a hole transport layer, or situated between a photogenerating layer, and a supporting substrate, a photoconductive composition, comprised of the squaraine compositions prepared in accordance with the process of the present invention.
Photoconductive imaging members containing specific squaraine compositions, particularly hydroxy squaraines, are well known. Also known are layered photoresponsive devices with photogenerating layers and transport layers, reference U.S. Pat. No. 4,265,990. Examples of photogenerating layers disclosed in this patent include trigonal selenium, and phthalocyanines, while examples of transport layers that may be selected are comprised of certain diamines dispersed in an inactive resinous binder composition. Moreover, the use of certain squaraine pigments in photoresponsive imaging devices is disclosed in a copending application now U.S. Pat. No. 4,415,639, the disclosure of which is totally incorporated herein by reference, wherein there is described an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer. As photoconductive compositions for this device, there can be selected various squaraine pigments, including hydroxy squaraine compositions of the formula as outlined on page 13, beginning at line 21 of the copending application. Additionally, there is disclosed in U.S. Pat. No. 3,824,099 certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent, the squaraine compositions are photosensitive in normal electrostatographic imaging systems.
In other copending applications, there are described the use of novel squaraine compositions of matter, such as bis-9-(8-hydroxyjulolidinyl) squaraine as imaging members. One of the imaging members contains a supporting substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconducting composition layer capable of enhancing or reducing the intrinsic properties of the photogenerating layer, which compositions are comprised of the novel julolidinyl squaraine materials disclosed in the copending application, and a hole transport layer.
Also disclosed in U.S. Pat. No. 3,617,270 are optically sensitized photoconductive layers which preferably contain zinc oxide as a photoconductor, the sensitivity of which remains unchanged as a result of storage, in view of the presence of 1,3 or 1,2-squaric acid methine dyes of the formula as illustrated in column 1, beginning at line 35; while U.S. Pat. No. 3,824,099, discloses sensitive xerographic devices containing a charge generating layer comprising a squaric acid methine dye, and a charge transport layer containing a tri-arylpyrazoline compound.
Processes for preparing squaraine compositions generally involve the reaction of squaric acid with an amine. Thus, for example, the novel julolidinyl squaraine compositions disclosed in the referenced copending application are prepared by the reaction at a temperature of from about 50 degrees Centigrade to about 130 degrees Centigrade of an aromatic amine and squaric acid, in a molar ratio of from about 1.5:1 to 3:1, in the presence of a mixture of an aliphatic alcohol and an optional azeotropic cosolvent. About 200 milliliters of alcohol per 0.1 mole of squaric acid are used, while from about 40 milliliters to about 4,000 milliliters of azeotropic material are selected. Illustrative examples of amine reactants include 8-hydroxyjulolidine, while examples of aliphatic alcohols selected include 1-butanol. Azeotropic materials used include aromatic compositions such as benzene and toluene.
While the above processes for preparing squaraine compositions may be suitable for their intended purposes, there continues to be a need for other processes wherein photoconductive squaraine compositions, can be prepared. Additionally, there remains a need for simple, economical processes for preparing squaraine compositions wherein the products obtained contain impurities therein. While it is not desired to be limited by theory it is believed that the presence of impurities in the squaraine compositions resulting from the process of the present invention causes the photosensitivity of these compositions to increase. Furthermore, there continues to be a need for the preparation of squaraine compositions of enhanced photosensitivity when these compositions are selected for layered photoresponsive imaging devices. Moreover, there remains a need for processes for preparing certain squaraine compositions of enhanced photosensitivity, wherein the resulting products when incorporated into imaging members exhibit excellent dark decay and high charge acceptance values.